CLIMATIC WARMING MAY EXACERBATE EUTROPHICATION IN PARTIALLY MIXED ESTUARIES: THE HUDSON RIVER EXAMPLE

Most GCM models predict that global warming will lead to large changes in transport of water in rivers in the northeastern US, with much less discharge during the summer and perhaps greater discharge in winter and early spring. This may have profound effects on estuaries in the region, both due to changes in delivery of nutrients from the watershed and due to changes in estuarine circulation. Many of the estuaries in the northeastern US are partially mixed estuaries, in which stratification and mixing are quite sensitive to changes in freshwater discharge from rivers into the estuaries. Over the past 5 years, we have studied how changes in freshwater discharge to one such estuary -- the Hudson River -- affect primary production. Production in the Hudson is generally light limited, in large part because of deep mixing. However, during periods of low freshwater discharge, stratification in the estuary increases, which reduces the effect of light limitation by increasing the time phytoplankton are maintained in the photic zone. This leads to large increases in rates of primary production and to decreases in dissolved nutrients, particularly phosphorus. Global warming may greatly exacerbate eutrophication in the Hudson and similar estuaries.